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And now for something thatâs not about dino-puke. Two dino-listers posted
questions after my last email about ornithischian cheeks, and I apologize
for taking so long to respond, as well as forgetting who asked the

The first questioner asked if I knew of any drawings on the internet that
were an accurate portrayal of ornithischian cheeks. The only drawing I
could find that portrayed an open mouthed ornithischian with cheeks that are
drawn in a way I believe to be correct, is a drawing by myself (shameless
self promotion) depicting Parksosaurus warrenae. The drawing can be viewed


If I were to revise the drawing today, I would have made the cheeks even
more restricted and probably with more wrinkles.

The second questioner asked my opinion of Steven Czerkasâ restoration of a
cheekless and turtle-beaked Stegosaurus stenops. My opinion is this: the
restoration is almost certainly incorrect, and his methodology is extremely
flawed for a number of reasons.

He relied upon two lines of evidence. The first being a morphoclinic
reduction in tooth size (versus skull size I imagine) from basal
ornithischians such as Lesothosaurus, to basal stegosaurs like
Huayangosaurus to S. stenops itself. There are not very many stegosaurid
skulls with teeth known, in comparison to the amount of body fossils, so itâs
little suspect to extrapolate a trend based on Huayangosaurus, Paranthodon,
Stegosaurus, and Tuojiangosaurus, especially when no coherent idea of the
internal systematics of the Stegosauridae exists. Additionally, Czerkas
doesnât explain if there is also a reduction in absolute size of the teeth
or just the tooth to skull ratio, which may indicate that these animals were
just getting bigger.

He uses the morphoclinic trend to predict that stegosaurids, had they lived
past the early Cretaceous would have become toothless. This is extremely
suspect, because although morphoclinic trends are kind of neat, there is
absolutely no predictive power in them:Â You canât use past trends to insist
on a conclusion that might have happened, especially if the evidence is

The morphoclinic trend seems to show a rough pattern of the invisible hand of
the creator of the universe, but since all stegosaurs died before the late
Cretaceous, you can't be sure that the same selective pressures would have
driven the invisible hand of the creator of the universe to continue the
morphoclinic trend.

The second piece of evidence Czerkas uses to support his turtle-beaked
Stegosaurus theory is a skull of S. stenops which, although beautifully
preserved, has undergone quite a bit of crushing and deformation. On the
animalâs left side, the lower jaw appears to have rim or ridge that is
lateral to the
tooth row and actually obliterates the teeth from lateral view at the very
back of the jaw. Czerkas postulated that this ridge supported an extension
of the predentary rhamphothica, and that the entire snout was basically one
long beak.

What Czerkas failed to mention, and continues to fail to mention, is that
that ridge is the result of crushing. If he were to simply look on the
right side of the very same skull, he would not see a ridge. As far as I
know, no other specimens of S. stenops have the ridge and no other
stegosaurids have any ridges either.

Add that evidence, to the evidence I previously cited concerning cheeks
probably existing in ankylosaurs, the sister taxon to stegosaurs within
Thyreophora, parsimony would insist that they too, had cheeks.

Pete Buchholz

"Rarely is the question asked: is our children learning?"
-------'President' George W. Bush